This invention relates to electric furnaces and is more particularly concerned with cooling electric arc furnaces externally so as to minimize erosion of the refractory furnace lining resulting from localized heating and arc flaring.
In one type of electric arc furnace the electrodes are held in spaced relationship with the molten bath in the furnace and an electric arc is drawn between the electrodes and the bath to provide heat for processing the metal.
Electric arc furnaces are variously designed for using one or more electrodes and the electrodes may be supplied with alternating or direct current. Some arc furnaces use consumable electrodes of graphite or carbon and others use non-consumable electrodes which may be constructed of refractory materials and partially of metallic components on which the arc is struck.
When an electric arc furnace is operating, the refractory lining of the furnace is subjected to heat which is radiated from the melt and the arc and there is often localized heating resulting from the arc flaring and directly contacting the refractory. Localized overheating in certain zones results in rapid deterioration and erosion of the refractory in these zones. This is a well known occurrence in electric arc furnaces and it has received much attention because localized erosion compels rebuilding of the furnace lining prematurely.
Attempts to minimize the adverse effects of arc flaring and localized overheating have involved controlling the bath temperature, optimizing the distance between the bath and electrodes to obtain a more stable arc and by controlling the applied voltage. Another proposed solution to the problem has been to use non-consumable electrodes that are provided with electromagnets which produce a magnetic field that causes the arc generated by the electrode to rotate and thereby reduce the time during which it dwells on any surface area of the refractory.
On some occasions, the outer shell of the electric arc furnace is provided with a coolant chamber for taking the heat away from the shell and adjacent refractory lining as rapidly as possible. However, prior art furnace cooling means have not been fully effective to minimize thermal deterioration and erosion since there is usually metal-to-metal contact between the cooling jacket and the furnace shell such that any irregularity between the interfacing surfaces produces interstices which are occupied by air which has poor thermal conductivity.